Alastair Hunter, vice chairman of the University and College Union, warned some gap year students may be "forced to take run of the mill jobs that won't add to their educational experience".
Ben Whittaker, of the National Union of Students, also pointed out the risks of taking a gap year.
"These students will be competing with next year's cohort to get into university and I think for the government to be saying 'go out into the world go and get work experience' in a time of economic recession is absolutely ludicrous."
The increased pressure on university places is thought to be due to a bulge in the population (there are more 18-year-olds this year), the drive to get more young people into higher education and the effects of the recession encouraging both young and old to go to university.
Higher Education Minister David Lammy said record numbers of people were taking advantage of the highest-ever level of funded places on offer.
"Students who don't qualify for their offer should not panic though, they can apply for places through the clearing system, reapply the following year or seeking work experience or training supported by our Backing Young Britain campaign," he added.
Students who don't qualify for their offer should not panic
Higher Education Minister David Lammy
Shadow universities secretary David Willetts said the Conservatives have been calling for a "proper review of the funding of universities".
"The aim would be to ensure that we don't end up ever again in this absurd position where the government tries to control the detail of the exact number of places at each university, so that universities find themselves turning away well-qualified students," he said.
This year the overall pass rate for A-levels in England, Wales and Northern Ireland rose to the record level of 97.5%, adding to the clamour for places.
Students in Scotland, who received the results of their Highers earlier this month, had a head start on clearing. The pass rate for Highers also rose - by 0.8 percentage point to 74.2%.
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